The invention relates to an injection syringe with a barrel on whose one end a chuck surmounted by an injection needle can be attached, having a piston displaceable in the barrel, on which a piston rod protruding from the other end of the barrel and provided at its extremity with an operating handle is provided. A system on the chuck automatically locks the piston when the latter is advanced by a given amount in the direction of the needle to prevent withdrawal of the piston, and the chuck can be joined to the barrel by a rotational connection to be released by turning it in and in some cases by axial displacement of the chuck in the barrel. Antirotational members are on the chuck and piston, which, when the piston is pushed forward toward the chuck, interact to lock the piston on the chuck, and by the rotation of the operating member permit a release of the rotational connection and then a withdrawal of the piston, chuck and needle into the cylinder over their entire length. The antirotational members are projections at angular distances from one another and can be brought by axial displacement of the piston into mutual, meshing engagement.
An injection syringe of this kind is disclosed in European Patent Application, publication No. 402,908. In this injection syringe the chuck can relatively easily be released from its rotational connection to the barrel.
Often medicaments have to be drawn into injection syringes by means of a needle which has to pierce a closure, say of rubber or plastic, before it can penetrate into the vessel containing the medicament. For this purpose a comparatively strong needle has to be used , which usually has a comparatively large inside diameter. The result is that components of the pierced closure, such as rubber or plastic particles, can be drawn into the injection syringe. In no way are such particles to be injected. For this reason the needle serving to draw in the medicament must be replaced by a needle with a smaller inside diameter. When such a replacement is made, if a syringe of the kind described above is used, it is possible that the chuck might loosen a little and allow medicament to escape between the chuck and the barrel.